Garett Rogers at Googling Google covers Google's "Trusted Tester Program," a preexisting invite-only program that now appears to have gained a formal FAQ left open to public view.
The program lets friends and family of Google employees test new software. The select few login here to access programs. More helpful to anyone is the Google Trusted Tester Program FAQ, which explains the program in more detail. Somewhat amusingly, those in the program aren't even allowed to discuss that it exists despite the fact that the FAQ has been left open to public viewing.
Dirson's blog had mention of this program back last August, but no FAQ was apparently posted then. Google's also long allowed friends and family of Googlers to test beta software. Google Desktop, for example, went out for friends and family testing in February 2004, as covered in the SEW members edition of the Google Desktop launch article:
As for the Google Desktop project, it has been in development for the past year, Google said. The first testing version went out to some within Google in February. Further versions followed, with a release candidate sent to 2,000 Google employees and trusted friends and family.